Rontgen tube



July 3, 1951 B. v. VALTERSSON 2,559,136

R'cSNTGEN-TUBE Filed Feb. 21, 1946 Zn/dental 130ml 1155011, 17a liezss 012/ l l atented July 3, 1951 RoNTGEN TUBE.

Bo Valterson Valtersson, Stockholm, Sweden, assignor to Jarnhs Elektriska Aktiebolag, Stockholm, Sweden Application February 21, 1946, Serial No. 649,452 In Sweden February 23,1945

8 Claims.

For the generation of the relatively high tensions, 30-200 kilovolt,- required for the operation of R-iintgen-apparatus, ordinary low frequency alternating current and transformers would generally be made use of hitherto. According to the present invention, high-frequency alternating current is used instead, the alternating voltages being supplied to the electrodes of the Rontgentube through the agency of one or more resonators. Here, the electrodes are preferably arranged within the resonator in suchmanner that the resonator will at the same time form the actual Rontgen-tube. The arrangement involves the advantage that the mode of operation of the Rontgen-tube and the Rontgen-radiation may be controlled more readily than is the case in voltage generators of the type hitherto used. Thus the high-frequency source of alternating current may be controlled by simple means, so that the resonator operates intermittently, an intermittent Rontgen-radiation being thus obtained, which may be utilized, for instance, for the examination or illustration of moving objects.

The invention will be described in the following with reference to the accompanying drawing. Figure 1 shows a longitudinal section through a Rontgen-tube according to the invention together with the high-frequency generator connected thereto. Figure 2 is a longitudinal section representing another form of embodiment of the Rontgen-tube, and Figure 3 is a cross section through the plane of symmetry of the tube. Figure 4 shows the latter tube, viewed from above, Figure 5 shows the cathode on a larger scale, and Figure 6, a cross-section, of a slightly modified form of the invention.

In the embodiment shown" in Figure 1, the Rontgen-tube consists of a resonator of the oscillatory line type with coaxial external and internal conductors. It consistsof a hermetically closed and preferably evacuated cylindrical vessel I of metal. The vessel may, however, be made of some other material having the requisite mechanical strength and good evacuating properties, for instance, glass provided with an inner metallic coating. Also ceramic material may be used provided with an inner coating of metal. The end portions of the vessel are formed into cylindrical tubes 2, 3 coaxially arranged rela-. tively to the external cylindrical jacket, said tubes being open at the extreme ends thereof,

while the inner closed ends 4, 5 of the tubes form the two electrodes. The electrode 4, which constitutes the cathode, has abowl-shaped end portion 6, in which the incandescent filaments l are 2. arranged whereas the'electrode 5, which constitutes the anode, is in the ordinary manner provided with a-focal spot 8-consisting of a very high-ohmic material, such as tungsten; in the formof a plate, which ismelted into the'glass and arranged obliquely in such manner that the electrodes impinging upon the focal spot generate Rontgen-rays, which may-be emitted from the tube in the transverse direction thereof through a window 9, which may consist of aluminium or similar metal having a great perviousness to the Rontgen-rays. If the resonator consists of glass or similar non-conducting'materiaL'the same is provided on the inside or over the surface thereof with a thin coating of a material which is highly conductive for highfrequency currents, such as silver, which may be applied either chemically or by cathode atom ization. Theheating current is supplied through a two-wire conductor, the one lll'of the con ductors is connected to the incandescent'fila ments 1, while the other conductor II is connected, like thecorresponding ends of the-incandescent filaments, to the conductive-coating onthe inside of the tube. The anode may be cooled by means of a cooling liquid supplied through pipe connections l2, l 3and caused by a partition [4 inserted into the tube 3 to flow in contact with the inside of the electrode. The cathode may also be cooled ina similar manner.

Any high-frequency generator my be used as a source of high-frequency currents,- said generator being designated by A in the drawing; Preferably, a tube oscillator is made use of,'with or without an output amplifier. A magnetron; klystron or'similar'generator may also be used. The generator, which delivers an alternating voltage of a frequency equalling the proper frequency of the resonator, must be constructed for a comparatively large output. The alternat ing voltage is supplied directly, orthrough an adapted low-ohmic conductor, to the metallic coating of the resonator, the live conductor I5 being introduced through-a vacuum-tight fitting IS. The adapted low-ohmic conductormay be a coaxial conductor or consist of twoparall'el conductors. The connection" between the high frequency generator and the resonator may also be effected magnetically through a circuit pro jecting into the interior of the resonator,- which circuit may continue externally in a straight con ductor toform a half-wave antenna'with the resonator, said antenna receiving energy from an adjacent antenna directed toward thesame; Energy is supplied to the high-frequency genaid of a control device C, the energy delivered to the resonator, and thus the Rontgen-radiation may be controlled quantitatively and qualitatively. By controlling the bias of the oscillator, the latter may be brought out of oscillation in a veryshort time, and may be brought into oscillation just assoon. Hereby the resonator may be caused to operate intermittently to generate an intermittent Rontgen-radiation, so that moving objects may be examined or photographed. S'witching-in and disconnection of the oscillatory energy may then be controlled by mechanical, optical, magnetic or photo-electric relays cooperating with the movable object.

As stated above, the resonator shown is of the type with coaxial conductors, the conductive coating on the outside of the tubes 2, 3 forming the inner conductor, while the coating on the inside of the cylinder l forms the outer conductor. It may beregarded as composed of two quarterwave resonators corresponding each to one half of the tube and forming together a half-wave resonator. Thus the length of the tube is approximately equal to the half of the wave length of the resonance frequency. To reduce the constructive length of the tube, the latter may be bent, so that the two halves will be situated beside one another, as shown in Figures 2 to 4.

The window 9 will then be located so that the Rontgen-radiation may be focused in the longitudinal direction, whereby certain practical advantages are obtained. With respect to the higher current density at the ends of the tube, these end portions are preferably flared in a conical fashion.

By constructing the resonator as a quarter- Wave resonator, the length of the tube may be reduced to the half, but at the same time the voltage bet-ween the electrodes will be reduced to the half, and consequently a half-Wave resonator is to be preferred in practice.

A good resonator of moderate dimensions is hardly obtainable for a wave length exceeding '3 meters. gard must be paid to the relation between the magnitude of the input and the running time of the electrons in the discharge gap of the resonator. At 300 megacycles it is believed to be rather diflicult to use high outputs with continuous feeding, and consequently it will be necessary to feed the resonator intermittently from an impulse-operated generator. By the use of an intermittent Rontgen-radiation, the dimensions of the resonator may thus be reduced.

The resonator may be connected on the outside to earth potential. Detrimental secondary radiation and other nondesirable radiation may be screened off by means of a layer of lead or other material absorbing the Rontgen-rays applied to the resonator. For similar purposes, and also for cooling, the tube may be entirely submerged in liquid.

To attain a maximum of step-up transformationof the alternating voltage supplied, and thus the highest possible voltages between the electrodes of the resonator, the latter should have a high impedance and a high Q-value, which is obtained by suitably dimensioning the internal and external conductors with the use of resonators with coaxial conductors.

In place of resonators of the oscillatory line type with coaxial conductors, resonators with parallel conductors may obviously be made use of. Other types of hollow space resonators with in- With smaller wave-lengths, special re- 4 wardly projecting electrodes, such rhumbatrons and spherical resonators may also be used.

The alternating voltages generated at the electrodes are of such magnitude that a Rontgenradiation of all frequencies required in practice may be obtained. Since the electrons are accelerated only during that half-cycle of the oscillation periods when the cathode is negatively charged, the apparatus hitherto described emits X-rays only during that half-cycle, whereas the other half-cycle is not utilized. According to an embodiment illustrated in Figure 6 each of the reentrant portions 2 and 3 is provided with a charge emitting cathode l and a charge collecting and X-ray emitting anode 8, whereby both halfcycles of the oscillation are utilized and an approximately continuous radiation will be obtained. The window 9 is in this case preferably so positioned as to allow X-rays from both anodes to pass therethrough.

I claim:

1. An electric discharge apparatus comprising a cavity resonator consisting of a closed envelope having a conductive inner surface, a source of high frequency energy, inductive coupling means for feeding high frequency energy into said resonator, two reentrant portions of said envelope forming inner conductors projecting from cpposite ends of the resonator cavity towards the center thereof and having conductive end surfaces facing each other, a charge emitting cathode providecl on the inner end of one of said reentrant portions in direct electric contact with the inner surface of the envelope, and a charge collecting and X-rays emitting anode provided on the inner end of the other reentrant portion in direct electric contact with the inner surface of the envelope.

2. An electric discharge apparatus as claimed in claim 1, in which the reentrant portions are extending centrally through the adjacent portions of the envelope and coaxially relatively to each other.

3. An electric discharge apparatus as claimed in claim 1, in which the reentrant portions are extending centrally through the adjacent portions of the envelope and at an angle relatively to each other.

4. An electric discharge apparatus as claimed in claim 1, in which the reentrant portions form tubular portions of the envelope having closed inner ends.

5. An electric discharge apparatus comprising a cavity resonator consisting of a closed envelope having a conductive inner surface conically tapered towards the center of the resonator cavity, two reentrant portions of said envelope forming inner conductors projecting from opposite ends of the resonator cavity and conically tapered towards the center of the cavity, a charge emitting cathode provided on the inner end of one of said reentrant portions in direct electric contact with the inner surface of the envelope, and a charge collecting and X-rays emitting anode provided on the inner end of the other reentrant portion in direct electric contact with the inner surface of the envelope.

6. An electric discharge apparatus comprising a cavity resonator consisting of a closed envelope having a conductive inner surface conically tapered towards the center of the resonator cavity, two reentrant portions of said envelope forming inner conductors projecting from opposite ends of the resonator cavity and conically tapered towards the center of the cavity, said reentrant portions being arranged centrally of the adjacent walls of the envelope and at an angle relatively to each other, a charge emitting cathode provided on the inner end of one of said reentrant portions in direct electric contact with the inner surface of the envelope, and a charge collecting and X-rays emitting anode provided on the inner end of the other reentrant portion in direct electric contact with the inner surface of the envelope.

7. An electric discharge apparatus comprising a cavity resonator consisting of a closed envelope having a conductive inner surface, a source of high frequency energy, inductive coupling means for feeding high frequency energy into said resonator, two reentrant portions of said envelope projecting from opposite ends of the resonator cavity towards the center thereof and having conductive end surfaces facing each other, each of said reentrant portions having a charge emitting cathode as well as a charge collecting and X-rays emitting anode provided on the inner end thereof.

8. An electric discharge apparatus comprising a cavity resonator consisting of a closed envelope having a conductive inner surface, a source of REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,154,368 Van Der Tuuk Apr. 11, 1939 2,275,480 Varian et al. Mar. 10, 1942 2,342,789 Cassen Feb. 29, 1944 2,392,379 Hansen Jan. 8, 1946 2,392,380 Varian Jan. 8, 1946 

